Add XSLTHL EBNF Syntax Definition

[tajmone]

Although optional, we could add an EBNF syntax highlighting definition, just to add some color to BNF rules (nothing dramatic, just slight shades variations of the base color).

NOTE — The rules in the Alan Manual actually use EBNF notation (not BNF), so I should change the source language to ebnf to correctly support the syntax definition, especially since other HTML highligthers ship with both BNF and EBNF definitions, and having the wrong lang definition might cause problems.

• Create custom language definitions fo XSLTHL:
  • EBNF.
• Manual AsciiDoc source: Change BNF to EBNF in source blocks.